This invention relates to a golf club which has a club head with a face comprising a metallic glass, namely, a so-called amorphous alloy face exhibiting excellent ball hitting properties. More specifically, this invention relates to a golf club which has a club head with a metallic glass face (amorphous alloy face) of desired shape exhibiting excellent strength properties owing to absence of the so-called cold shut which is the region that became amorphous alloy by meeting of the molten metal surfaces.
Various methods for producing amorphous alloys have been proposed. Exemplary such methods include the method wherein a molten metal or alloy in liquid state is solidified by quenching and the resulting quenched metal (alloy) powder is compacted at a temperature below the crystallization temperature to produce a solid of the predetermined configuration having the true density; and the method wherein a molten metal or alloy is solidified by quenching to directly produce an ingot of the amorphous alloy having the predetermined configuration. Almost all amorphous alloy produced by such conventional methods had an insufficiently small mass, and it has been impossible to produce a bulk material which can be used in golf club face by such conventional methods. Another attempt for producing a bulk material is solidification of the quenched powder. Such attempt, however, has so far failed to produce a satisfactory bulk material.
For example, the amorphous alloy produced in small mass have been produced by melt spinning, single roll method, planar flow casting and the like whereby the amorphous alloy in the form of thin strip (ribbon) in the size of, for example, about 200 mm in the strip width and about 30 xcexcm in the strip thickness are produced. Use of such amorphous alloys for such purposes as the core material of a transformer has been attempted, but so far, most amorphous alloys produced by such methods are not yet put to industrial use. The techniques that have been used for solidification forming or compaction molding the quenched powder into an amorphous alloy of a small mass include CIP, HIP, hot press, hot extrusion, electro-discharge plasma sintering, and the like. Such techniques, however, suffered from the problems of poor flow properties due to the minute configuration, and the problem of temperature-dependent properties, namely, incapability of increasing the temperature above the glass transition temperature. In addition, forming process involves many steps, and the solidification formed materials produced suffer from insufficient properties as a bulk material. Especially, high strength, high toughness and other properties required for the face of a golf club can not be obtained. Therefore, such methods are still insufficient.
Recently, the inventors of the present invention found that a number of ternary amorphous alloys such as Lnxe2x80x94Alxe2x80x94TM, Mgxe2x80x94Lnxe2x80x94TM, Zrxe2x80x94Alxe2x80x94TM, Hfxe2x80x94Alxe2x80x94TM and Tixe2x80x94Zrxe2x80x94TM (wherein Ln is a lanthanide metal, and TM is a transition metal of the Groups VI to VIII) ternary systems have low critical cooling rates for glass formation of the order of 102 K/s, and can be produced in a bulk shape with thickness up to about 9 mm by using a mold casting or a high-pressure die casting method.
It has been, however, impossible to produce a large-sized amorphous alloy material of desired configuration irrespective of the production process. There is a strong need for the development of a new solidification technique capable of producing a large-sized amorphous alloy material and an amorphous alloy having a still lower critical cooling rate for enabling the production of the amorphous alloy of larger size.
In view of such situation, the inventors of the present invention proceeded with the investigation of the bulk amorphous alloy using the ternary alloy by focusing on the effect of increasing the number of the alloy constituents each having different specific atom size as exemplified by the high glass formation ability of the ternary alloy primarily attributable to the optimal specific size distribution of the constituent atoms that are mutually different in size by more than 10%. As a consequence, the inventors found amorphous alloys of Zrxe2x80x94Alxe2x80x94Coxe2x80x94Nixe2x80x94Cu alloy systems, Zrxe2x80x94Tixe2x80x94Alxe2x80x94Nixe2x80x94Cu alloy systems, Zrxe2x80x94Tixe2x80x94Nbxe2x80x94Alxe2x80x94Nixe2x80x94Cu alloy systems, and Zrxe2x80x94Tixe2x80x94Hfxe2x80x94Alxe2x80x94Coxe2x80x94Nixe2x80x94Cu alloy systems that have significantly lower critical cooling rates in the range of from 1 to 100 K/s, and disclosed in U.S. Pat. No. 5,740,854 (Unites States Patent corresponding to JP-A 6-249254) that alloys of. Zrxe2x80x94Alxe2x80x94Nixe2x80x94Cu alloy systems may be produced into a bulk amorphous alloy material with a size of up to 16 mm in diameter and 150 mm in length by quenching the melt in a quartz tube in water.
The inventors of the present invention also disclosed in U.S. Pat. No. 5,740,854 and JP-A 6-249254 that the resulting bulk amorphous alloy material has a tensile strength of as high as 1500 MPa comparable to the compressive strength and break (crack) accompanying serrated plastic flow in the tensile stress-strain curves, and that such high tensile strength and serrated plastic flow phenomenon result in excellent malleability despite the large thickness of the bulk amorphous alloy produced by casting.
On the bases of the above-described findings of the bulk amorphous alloy production, the inventors of the present invention have continued an intensive study to thereby develop a method that is capable of producing a glassy metal material of even larger size with various configurations by a simple procedure. As a consequence, the inventors proposed a process for producing metallic glass by suction casting wherein an amorphous alloy of large size having excellent properties can be readily produced in simple operation by instantaneously casting the molten metal material in a mold cooled with water.
Such process of metallic glass production by suction casting as disclosed in U.S. Pat. No. 5,740,854 and JP-A 6-249254 is capable of producing a columnar bulk amorphous alloy, and the thus produced columnar bulk amorphous alloy exhibits good properties. In this prior art process, however, the bottom of the water cooled crucible is moved downward at a high speed and the molten metal is instantaneously cast into a vertically extending water-cooled mold to thereby attain a high moving speed of the molten metal and a high quenching rate.
In such production process, the molten metal is fluidized with the surface of the molten metal becoming wavy, and the surface area of the molten metal is increased with the increased surface area contacting the outer atmosphere. In some extreme cases, the molten metal is fluidized into small separate bulk molten metal droplets before being cast into the vertically extending mold. Therefore, the surfaces of the molten metal often meet with each other upon casting of the molten metal into the vertically extending water-cooled mold, and the so called cold shuts or discontinuities are formed at the interfaces of the thus met interfaces. The resulting bulk amorphous alloy thus suffered from inferior properties at such cold shuts, and hence, the bulk amorphous alloy as a whole suffered from poor properties.
In addition, the metal material is melted in a water-cooled hearth, and the part of the metal in contact with the hearth is at a temperature below the melting point of the metal material even if the metal material is in molten state. The part in contact with the hearth, therefore, is likely to induce nonuniform nucleation. In the above-described suction casting, such part of the molten metal which may induce uniform nucleation is also cast into the vertically extending water-cooled mold and there is a fair risk of crystal nucleus formation in the corresponding part.
Furthermore, since the bottom of the water-cooled crucible is moved downward at a high speed, the process suffered from a fair chance of the molten metal entering into the gaps formed between moveable parts and the like to reduce the reproducibility. In some extreme cases, the entering molten material is even caught in such gaps and resulted in failure, stop, or incapability of operation.
In the meanwhile, use of an amorphous alloy material for the face of a golf club has been proposed since the clubface is required to have high strength, high toughness, and high impact strength, and golf clubs wherein an amorphous alloy is used for the face insert are commercially available and attention is being given to such golf clubs. Production of such golf club, however, has been associated with the problem of low yield of the amorphous alloy face free from defects such as cold shuts, and variation in the mechanical properties of the face due to the molding procedure. The golf club, therefore, suffered from high price of the face, variation in the properties, and high cost.
An object of the present invention is to obviate the problems of the prior art as described above, and to provide a golf club which has excellent club properties and which has an amorphous alloy clubface of desired shape free from the so-called cold shuts, that is the amorphous region formed by the meeting of the molten metal surfaces that has been cooled to a temperature below the melting point through contact with outer atmosphere. Preferably, the clubface is also free from crystalline region formed by growth of crystalline nucleus through nonuniform nucleation of the molten metal at a temperature below the melting temperature. Another object of the present invention is to provide a golf club which has been produced by a simple, single-step, highly reproducible process wherein the molten metal at a temperature above the melting point is selectively cooled at a rate higher than the critical cooling rate. A further object of the present invention is to provide a golf club which has excellent strength properties including high strength and high toughness as well as excellent shot properties realized by improving restitution efficiency upon hitting of the golf ball whereby the initial speed of the golf ball is increased to its maximum.
In order to attain the objects as described above, there is provided by the present invention a golf club with a club head having a metallic glass face wherein
said metallic glass face is a metallic glass face of desired shape produced by filling a metal material in a hearth; melting said metal material by using a high-energy heat source which is capable of melting said metal material; pressing said molten metal which is at a temperature above the melting point of said metal material to deform the molten metal into the desired shape by at least one of compressive stress and shear stress at a temperature above the melting point, while avoiding the surfaces of the molten metal which are cooled to a temperature below the melting point of said metal material from meeting with each other during the pressing; and cooling said molten metal at a cooling rate higher than the critical cooling rate of the metal material simultaneously with or after said deformation to produce the metallic glass face.
The metallic glass face may preferably have a Vickers hardness of at least 300 Hv.
The metallic glass face may preferably have a Young""s modulus in the range of 50 GPa to 150 GPa.
The metallic glass face may preferably have a thickness in the range of 1.5 mm to 4.5 mm.
The metallic glass face may preferably have a value of the product Exc3x97T of Young""s modulus E (GPa) and thickness T (mm) in the range of 100 to 350.
The metallic glass face may preferably have a tensile strength of at least 1000 MPa.
There is also provided by the present invention a golf club wherein said molten metal at a temperature above the melting point of said metal material is pressed while avoiding not only the meeting of the surfaces of the molten metal which are cooled to a temperature below the melting point of said metal material with each other but also meeting of such molten metal surface with another surface cooled to a temperature below the melting point of said metal material.
The pressing and deforming of said molten metal is preferably accomplished by selectively rolling said molten metal which is at a temperature above the melting point of said metal material into plate shape or other desired shape with a cooled roll for rolling mounted on said hearth, while cooling simultaneously.
The metallic glass face is preferably a metallic glass face of plate shape or other desired shape produced by, after melting said metal material filled in the hearth, selectively rolling the molten metal which is at a temperature above the melting point rising over the hearth with simultaneous cooling by rotating said cooled roll and moving the hearth in relation to said high energy heat source and said cooled roll for rolling.
The hearth is preferably of elongated shape, and the metallic glass face comprises a plurality of metallic glass faces of plate shape or other de sired shape produced by continuously conducting the melting, the rolling of the molten metal which is at a temperature above the melting point, and the cooling by using said hearth of the elongated shape and moving said hearth in relation to said high energy heat source and said cooled roll for rolling to thereby serially produce metallic glass faces.
The cooled roll for rolling is preferably provided at the position corresponding to the hearth with a molten metal-discharging mechanism for discharging the molten metal which is at a temperature higher than the melting point from the hearth, said molten metal-discharging mechanism being fabricated from a material having low thermal conductivity.
The pressing and deforming of said molten metal is preferably accomplished by selectively transferring said molten metal which is at a temperature above the melting point of said metal material into a cavity of the desired shape in the mold provided near said hearth without fluidizing the molten metal, and pressing the molten metal with a cooled upper mold without delay to forge the molten metal into the desired shape together with simultaneous cooling.
The metallic glass face is preferably a metallic glass face of the desired shape produced by, after melting said metal material filled in the hearth, moving said hearth and said lower mold to right underneath said upper mold and descending the upper mold toward the lower mold without delay to thereby selectively transfer the molten metal which is at a temperature above the melting point into said lower mold where the molten metal is pressed and cooled for forging.
The upper mold is preferably provided at the position corresponding to the hearth with a molten metal-discharging mechanism for discharging the molten metal which is at a temperature higher than the melting point from the hearth, said molten metal-discharging mechanism being fabricated from a material having low thermal conductivity.
In the present invention, the phrase xe2x80x9cmeetingxe2x80x9d of xe2x80x9cthe surfaces cooledxe2x80x9d means the xe2x80x9cmeetingxe2x80x9d of xe2x80x9cthe surfaces of the molten metal (which are) cooled to a temperature below the melting point of said metal materialxe2x80x9d in a narrower sense. In a broader sense, this phrase also include the case wherein xe2x80x9cthe surfaces of the molten metal (which are) cooled to a temperature below the melting point of said metal materialxe2x80x9d meet with xe2x80x9cother surfaces cooled to a temperature below the melting point of said metal materialxe2x80x9d such as the surface of the hearth cooled by water. It should be noted that the phrase xe2x80x9cthe surfaces of the molten metal (which are) cooled to a temperature below the melting point of said metal materialxe2x80x9d are the surfaces of the molten metal (which are) cooled to a temperature below the melting point by contact with outer atmosphere, mold, hearth or the like.
The phrase xe2x80x9cpressing a molten metal (which is) at a temperature above the melting point of said metal material to deform the molten metal, while avoiding the surfaces cooled to a temperature below the melting point of said metal material from meeting with each other during the pressingxe2x80x9d used herein does not only mean the pouring of the molten metal maintained at a temperature above the melting point from the cooled hearth into the mold followed by pressing, while avoiding the formation of cold shuts which are formed by the meeting of the surfaces cooled to a temperature below the melting point of said metal material caused by fluidization or surface wave-formation. This phrase also includes use of a mold fabricated from a material such as quartz which is not thermally damaged at a temperature above the melting-point of the metal material, and heating of the lower mold to a temperature near the melting point, preferably, to a temperature above the melting point, followed by pouring of the metal molten with a high energy source, for example, a radio frequency heat source and maintained at a temperature above the melting point into the preliminarily heated lower mold without forming any surface which is cooled to a temperature below the melting point; and pressing with the cooled upper mold to thereby conduct the pressing and quenching at a rate above the critical cooling rate. Namely, if the metal material used is a material with an extremely low critical cooling rate, the metal molten in a quartz tube may be directly poured and cooled in water while maintaining its shape.
In other words, the cold shuts are formed when the pressing, deformation, compression., shearing of the molten metal are not conducted at a rate higher than the critical cooling rate and meeting of the cooled surface are not avoided. When a metal having a certain critical cooling rate, for example, 10xc2x0 C./sec is used, an amorphous bulk alloy without cold shuts can be produced only when the time between the molten state and the deformation and the decrease in temperature attain the predetermined critical cooling rate (higher than 10xc2x0 C./sec in this case); and the meeting of the cooled surface is avoided.
The term xe2x80x9cdesired shapexe2x80x9d used herein refers to the shape of a clubface in view of the embedding of the face insert constituting the club head face and fixing with a fastener. This term is not limited to any particular shape as long as the metallic glass material has a shape proper for the clubface and is formed into clubface through pressing or forging by using an upper press roll or forging mold of various contour and a lower press surface or forging mold of various contour which are controlled and cooled in synchronism. Exemplary shapes include, a plate, an unspecified profile plate, a cylindrical rod, a rectangular rod, and an unspecified profile rod.